Systematic initial embodied carbon assessment of concrete modular high-rise residential buildings: A case in Hong Kong

Reducing carbon emissions from buildings is essential to achieving carbon neutrality. Modular construction (MC) has been adopted as an innovative approach to improve construction sustainability. However, detailed embodied carbon (EC) assessment of concrete modular high-rise residential buildings is lacking. This study aims to systematically assess the cradle-to-end-of-construction EC of concrete modular high-rise residential buildings. A multilevel EC assessment model was proposed and validated to assess the EC at different spatiotemporal levels. A concrete modular high-rise staff quarters building was selected for case study. Its cradle-to-end-of-construction EC was quantified as 569.3 kgCO2e/m2 with around 80 % from material production. The structural modules with structural walls generated more EC than the nonstructural modules. The residential area comprising the modules had higher EC emissions than the communal area. The case building generated 14.6 % less cradle-to-site EC from the production and transportation of structural materials but 20 % more cradle-to-end-of-construction EC compared with two prefabricated panelized building counterparts, respectively. The cradle-to-end-ofconstruction EC of the case building was reduced by 8.3 % by eliminating the nonstructural module floor and by 16.7 % by further decreasing the nonstructural module walls. The results show that concrete MC reduces the EC at the construction stage but does not necessarily achieve a lower initial EC than its conventional counterpart. Resolving the double-panel issues can effectively mitigate the EC of modular buildings. These findings demonstrate the effectiveness of the proposed multilevel EC assessment model and provide valuable insights for future research on the systematic EC assessment and reduction of modular buildings.